The
field of quantum computing has progressed significantly over the last few years
with companies such as IBM and Google pouring in substantial resources in
research and development. Despite the advancements, quantum computing has been
limited to only affluent organizations due to a dearth of candidate material
that can be used to drive quantum computers. But researchers at University of
Pennsylvania and the Indian Institute of Science Education and Research have
identified a material that makes a good candidate for use in quantum
computers. Harshvardhan Jog, a PhD fellow, along with Ritesh Agarwal,
professor of material science at the University of Pennsylvania have
discovered desired properties in the semimetal Ta2NiSe5 (also called TNSe).
Ideal
materials must show two key properties — quantum entanglement, a quantum state
when one particle is indistinguishable from the other, and coherence, the
property of a material that allows it to maintain entanglement. Coherence in
quantum computers is difficult to maintain and that is why quantum computing
remains elusive from the mainstream despite decades of research. Academia is
exploring complex material which possess desirable properties and TNSe is one
of them. Here is what a TNSe looks like in the macroscopic form:
The research was conducted under the guidance of Eugene Mele, Distinguished professor at the University of Pennsylvania and in collaboration with Luminita Harnagea, research scientist at Indian Institute of Science Education and Research (Pune). Harnagea also provided high-quality Ta2NiSe5 for the experiment while also contributing to studying the theoretical aspects of this.
As per 2D Semiconductors, Ta2NiSe5 is a semimetal that undergoes excitonic insulator transition at 330 kelvin (57°C or 134°F). In the excitonic insulator state, quantum materials undergo rapid condensation in a mechanism similar to Bardeen–Cooper–Schrieffer mechanism that applies to superconductors — although quite the opposite, leading to insulation instead of conduction. This condensation of the material limits the movement of the exciton (a combination of a free electron and a vacant hole in a semiconductor or a semimetal), leading to a coherence between quantum particles. Below you'll find a rather odd-looking but on-point YouTube video explaining the phenomenon in detail.
Coherence
relies on the principle that every particle has a wave-like behavior and if the
wave is split into two, then the waves may interfere with each
other coherently in a way that they superimpose to form a single state, as
explained on Phys.org. This co-existence is what forms the basis of quantum
computing. Coherence is essential in quantum computing because unlike a
classic computer bit, which either exists in on state (1) or off state (0), a
Qubit or quantum bit can co-exist in multiple states simultaneously (think
Schrödinger's cat). This allows a quantum computer to process vast volumes of
data very quickly.
Jog and Agarwal used an probing technique called circular photogalvanic effect, in which a light signal is used to carry electric field. Although materials that demonstrate inversion symmetry, such as Ta2NiSe5, do not respond to circular photogalvanic effect, the researchers were surprised to see a signal being produced by the material. According to Physics Stack Exchange, inversion symmetry is the property of a crystalline material that is symmetric along a point. To envision this, one can image an infinitesimally small mirror placed at the origin in a 3D plot, and the reflection of a point will be visible in the diagonally opposite octant.
The
researchers concluded this behavior occurred because Ta2NiSe5 breaks symmetry
under low temperature. These conclusions align with previous research published
in the physics journal Physics Review Letters, in which a group of researchers
had established that Ta2NiSe5 undergoes "lattice distortion from an
orthorombic to a monoclinic phase" i.e. the lattic titls sideways creating
an oblique grid of atoms. The same shear is observed by Jog and Agarwal in
their lab.
This
research by Jog and Agarwal provides a new tool to the academia for researching
similar complex crystalline materials that may exhibit properties of quantum
entaglement and macroscopic coherance, both of which are essential for
quantum computing. Agarwal said that with the understanding of these complex
condensed states and "entangled states of matter," materials like
Ta2NiSe5 "can become natural platforms to do large-scale quantum
simulation."
Reference:
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